1. Field of the Invention:
The present invention relates to multiple glazings formed from at least two sheets of glass separated by a gas space, generally air, providing heat insulation. The invention also relates to a technique for obtaining such multiple glazings.
2. Discussion of the Background
Double glazing, or more generally multiple glazing, is gradually equipping the majority of recently constructed or older dwellings due to the improvement in heat and/or acoustical comfort and the energy savings which it provides.
Diffusion of double glazing, however, runs into a two-fold problem:
(a) first, it is still frequently a craftsman-like product with multiple manufacturing steps and is, therefore, relatively expensive,
(b) second, this type of glazing is difficult to adapt to old frames whose grooves only allow the introduction of a single sheet of glass.
Present double glazing is basically of two types which can be differentiated by the type of interposed cross-braced frame which maintains the sheets of glass apart.
In accordance with a first type, the cross-braced frame is composed of rigid metal profiles joined together, which are, for example, aluminum. In this case, the frame does not adhere to the sheets of glass and does not act as a seal, which is provided by the in situ injection of a peripheral polymerizing joint, for example polysulfide.
An improvement in this type of glazing with a rigid cross-braced frame is obtained if an organic joint is interposed between the frame and the glass, for example a polyisobutylene and/or butyl rubber-based joint, which essentially guarantees a seal against water vapor, with a second joint, for example in polysulfide which is more water-impermeable, reinforcing the seal. This type of double glazing, which for example is sold by Applicant under the trademark Polyglass.RTM., performs very well because it is remarkably water-tight but is relatively expensive.
For its manufacture, a frame with the dimensions of the glazing must be produced by fitting profiles together, filling the profiles with a drying agent, such as a molecular sieve, coating their two opposite external surfaces with a polyisobutylene and/or butyl rubber-based mastic, placing the frame prepared in this manner between two sheets of glass, injecting a peripheral joint, for example of polysulfide into the groove defined by the edges of the two sheets of glass on each side of the profile and polymerizing the polysulfide.
A second type of double glazing is composed by glazing not having a rigid cross-braced frame, but two peripheral joints, that is, an interior butyl rubber-cased cord which also acts as a separator for the sheets of glass and an exterior polysulfide joint. This type of glazing, sold by Applicant under the trademark Biver.RTM. and described, in particular, in French Pat. Nos. 2,294,313 and 2,294,140, enables automated industrial manufacture by replacing the manual operation of fitting together the profiles with automated in situ extrusion of a cord.
In addition, the butyl rubber-based cord, which is also called the butyl cord, adheres to the glass and forms a first sealing barrier. Therefore, as in the case of Polyglass.RTM., this guarantees a longer life for the glazing which is exposed on the one hand to the infiltration of rain water, in the case of a damp atmosphere, particularly when used for kitchens, bathrooms, etc., and to variations in climate, which, depending on the outside temperature, cause the interposed sheet of gas to dilate or to contract, thus producing breathing of the glazing which basically makes it fragile at the sealing joints.
This breathing of the multiple glazing constitutes a general problem for all multiple glazing and requires great precautions at the time of laying the peripheral joints so as to prevent leaks at the glass-joint interface, particularly in the angles. Care should also be taken to ensure that air bubbles are not imprisoned at the interface of the joints, bubbles which by expanding and contracting in turn could lead to a loss in sealing.
These manufacturing defects, the practical consequences of which only occur a few years after the final placing of the glazing can only be overcome by using very qualified personnel and staff responsible for checking the quality of the work after the manufacturing step; in other words, using an expensive infrastructure.